Runoff sources and land cover change in the Amazon: an end-member mixing analysis from small watersheds

TitleRunoff sources and land cover change in the Amazon: an end-member mixing analysis from small watersheds
Publication TypeJournal Article
Year of Publication2011
AuthorsNeill, Christopher, Chaves Joaquin E., Biggs Trent, Deegan Linda A., Elsenbeer Helmut, Figueiredo Ricardo O., Germer Sonja, Johnson Mark S., Lehmann Johannes, Markewitz Daniel, and Piccolo Marisa C.
JournalBiogeochemistry
KeywordsCattle pasture, Deforestation, Flowpaths, Overland flow, Principal components analysis, Soil solution
Abstract

The flowpaths by which water moves from watersheds to streams has important consequences for the runoff dynamics and biogeochemistry of surface waters in the Amazon Basin. The clearing of Amazon forest to cattle pasture has the potential to change The flowpaths by which water moves from watersheds to streams has important consequences for the runoff dynamics and biogeochemistry of surface waters in the Amazon Basin. The clearing of Amazon forest to cattle pasture has the potential to change mixing space determined by potential flowpath endmembers, suggesting that some water sources to streams were not sampled. The contribution of overland flow as a source of stream flow was greater in pasture watersheds than in forest watersheds of comparable size. Increases in overland flow contribution to pasture streams ranged in some cases from 0% in forest to 27–28% in pasture and were broadly consistent with results from hydrometric sampling of Amazon forest and pasture watersheds that indicate 17- to 18-fold increase in the overland flow contribution to stream flow in pastures. In forest, overland flow was an important contribution to stream flow (45–57%) in ephemeral streams where flows were dominated by stormflow. Overland flow contribution to stream flow decreased in importance with increasing watershed area, from 21 to 57% in forest and 60–89% in pasture watersheds of less than 10 ha to 0% in forest and 27–28% in pastures in watersheds greater than 100 ha. Soil solution contributions to stream flow were similar across watershed area and groundwater inputs generally increased in proportion to decreases in overland flow. Application of EMMA across multiple watersheds indicated patterns across gradients of stream size and land cover that were consistent with patterns determined by detailed hydrometric sampling.